Why do I never see engineers use BJT's for switching off supplies? I've seen many times where an engineer specs an expensive MOSFET in situations where the "On resistance" doesn't matter and the circuit they are switching off is well below general purpose current levels.

sometimes the voltage drop is important, sometimes the heat, sometimes the speed, sometimes ...

Do not jump the gun and say "unnecessary" for the design of others.

If you used a mosfet, you could reduce/omit the capacitor which gives you some very undesirable states while discharging after an "off" command, maybe you can live with them, maybe those you critisize can not. Also, there is quite a stress on the transistor when an "on" command suddenly tries to charge the cap, you may need current limiting to make your PNP stay alive"

Erik

PS I use no such designs, not defending myself.